10:00 AM - 10:15 AM
[SVC28-05] Detection of geothermal anomalies at Aso caldera using Landsat-8 thermal infrared images and comparison with seismic and volcanic activities
A previous study (Gunatilake, 2023) showed that magmatic fluids rising along the fractures generated by the 2016 Kumamoto earthquakes resulted in an increase in subsurface temperature and pore water pressure around the Aso caldera, which could be utilized as a new geothermal resource. Although numerical simulations based on actual subsurface structure and earthquake events were performed in this previous study, actual temperature measurements were not taken. Also, since these simulations were performed on 2D cross section, it is difficult to identify the area where subsurface temperature rises. The aim of this study is to verify the previous study and detected geothermal anomalies by estimating land surface temperatures before and after the 2016 Kumamoto earthquakes. By comparing the hypocenter distribution and surface displacement during the same period, we also investigated the relationship with earthquakes and volcanic activities.
We used thermal infrared images acquired by the Landsat-8 optical satellite to estimate land surface temperature. Using two TIR bands of Landsat-8 images, we applied a method called the split-window algorithm to estimate the surface temperature. We used SAR data acquired by the ALOS-2 satellite to estimate surface displacement. A method called interferometric SAR was used to analyze the surface displacement. For the hypocenter distribution, we used hypocenter data published by the Japan Meteorological Agency. The analysis area was around the Aso caldera in Kumamoto prefecture, which has been the subject of the previous study. To reduce the seasonal influence on the land surface temperature in the analysis, we used the difference from the average surface temperature within the analysis area for comparison.
The results of the land surface temperature images showed a widespread increase in surface temperature near the Futagawa fault, in the northwestern part of the Aso Caldera, after the earthquakes. However, the rise of the temperature was only temporary and a month later the temperature returned to the previous level. Considering the continuous rise in surface temperature suggested previously, we focused on the northwest of the Aso caldera to more delineate the zones where surface temperature continued to rise after the earthquakes. As a result, we detected regions where the surface temperature continued to rise in the Uchinomaki area in the northwestern part of the Aso Caldera. In this Uchinomaki area, horizontal slide and associated cracks were observed due to the 2016 Kumamoto earthquakes. From the above, the geothermal anomalies in this area were caused by rising magmatic fluid along cracks created by horizontal slides during the Kumamoto earthquakes.
In the area near Mt. Aso, we detected geothermal anomalies using the same method and found that the surface temperature continued to rise only in the crater. We interpreted that this may be a geothermal anomaly because of increased volcanic activity of Mt. Aso, as can be inferred from the explosive eruption of Mt. Aso on October 8, 2016. We further showed that there was no significant surface displacement for about one month after the eruption of Mt. Aso, followed by subsidence for about four months, and then uplift. We interpreted that after the eruption, subsidence occurred due to the decrease of materials in the volcanic gas and other substances, and that the subsequent surface uplift was caused by the accumulation of these materials. In addition, considering the distribution of hypocenters in 2017, there were many small earthquakes with epicenters deep below Mt. Aso, which were not seen before the eruption. We interpreted that the earthquakes were due to volcanic activities of Mt. Aso.
We used thermal infrared images acquired by the Landsat-8 optical satellite to estimate land surface temperature. Using two TIR bands of Landsat-8 images, we applied a method called the split-window algorithm to estimate the surface temperature. We used SAR data acquired by the ALOS-2 satellite to estimate surface displacement. A method called interferometric SAR was used to analyze the surface displacement. For the hypocenter distribution, we used hypocenter data published by the Japan Meteorological Agency. The analysis area was around the Aso caldera in Kumamoto prefecture, which has been the subject of the previous study. To reduce the seasonal influence on the land surface temperature in the analysis, we used the difference from the average surface temperature within the analysis area for comparison.
The results of the land surface temperature images showed a widespread increase in surface temperature near the Futagawa fault, in the northwestern part of the Aso Caldera, after the earthquakes. However, the rise of the temperature was only temporary and a month later the temperature returned to the previous level. Considering the continuous rise in surface temperature suggested previously, we focused on the northwest of the Aso caldera to more delineate the zones where surface temperature continued to rise after the earthquakes. As a result, we detected regions where the surface temperature continued to rise in the Uchinomaki area in the northwestern part of the Aso Caldera. In this Uchinomaki area, horizontal slide and associated cracks were observed due to the 2016 Kumamoto earthquakes. From the above, the geothermal anomalies in this area were caused by rising magmatic fluid along cracks created by horizontal slides during the Kumamoto earthquakes.
In the area near Mt. Aso, we detected geothermal anomalies using the same method and found that the surface temperature continued to rise only in the crater. We interpreted that this may be a geothermal anomaly because of increased volcanic activity of Mt. Aso, as can be inferred from the explosive eruption of Mt. Aso on October 8, 2016. We further showed that there was no significant surface displacement for about one month after the eruption of Mt. Aso, followed by subsidence for about four months, and then uplift. We interpreted that after the eruption, subsidence occurred due to the decrease of materials in the volcanic gas and other substances, and that the subsequent surface uplift was caused by the accumulation of these materials. In addition, considering the distribution of hypocenters in 2017, there were many small earthquakes with epicenters deep below Mt. Aso, which were not seen before the eruption. We interpreted that the earthquakes were due to volcanic activities of Mt. Aso.